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2007 Child Asthma Data: Technical Information

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Behavioral Risk Factor Surveillance System (BRFSS) Survey

In 2007, the BRFSS survey was conducted in all 50 states, the District of Columbia and in three US territories (Guam, Puerto Rico and the Virgin Islands).

In each area where interviews were conducted, respondents were randomly selected from non-institutionalized civilian adults (18 years of age or older) living in households with a telephone (Chapter 4, page 7 of the BRFSS User's Guide [PDF - 1.7 MB]).

Child asthma prevalence data are produced from the responses to questions on BRFSS Random Child Selection and Childhood Asthma optional modules. The randomly selected adult provided responses to the child asthma questions. If the adult reported that one or more children aged 17 years or younger lived in the household, then one of the children was randomly selected as the “Xth” child. Questions on the BRFSS Random Child Selection and Childhood Asthma optional modules were asked of the “Xth” child.

Thirty-five states or territories used both the BRFSS Random Child Selection and Childhood Asthma optional modules in 2007. These states or territories were.

Data Analysis

Data Used:

The BRFSS 2007 survey dataset was used to calculate prevalence estimates for all states that had the Random Child Selection & Childhood Asthma Prevalence modules included in the common questionnaire. For states that used one or more dual questionnaires for these two modules, questionnaire version specific datasets were used for analysis.

Where sep is the standard error of the prevalence percent and tv represents the student’s t distribution with v degrees of freedom.

Small Sample Size and Failure of Distributional Assumptions

When sample sizes for a particular state or territory was smaller than 50, the calculated standard error of the prevalence estimate might have been large relative to the point estimate of the prevalence value, which caused a wide 95% confidence interval. This sometimes caused the lower limit of the 95% confidence interval to be negative. In which case, the lower limit of the interval was set to zero.

In situations where the normal distribution approximation to the binomial distribution did not hold, values for the standard error and the 95% confidence interval of estimates were not provided, because these estimates are not reliable.

Table Conventions:

In the tables, states and territories are listed in Federal Information Processing Standard (FIPS) code order.